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The tides of Venus

Juno is about to peer under the clouds of Jupiter

Jupiter, as seen from my garden in Sydney. The spacecraft Juno will soon be getting a closer view. Andy Casely, CC BY-NC

You’ve all heard the Planets Suite, right? Seven classical pieces that Gustav Holst used to ‘describe’ each of the known planets.

I’ve always found the Jupiter piece a bit odd – the beginning is a little bit flippant for the grandest planet in our solar system, but the majestic tune that sits in the middle I find particularly wonderful.

That’s exactly the soundtrack that plays in my head when I think of the spacecraft Juno orbiting above the swirls of Jupiter’s clouds.

JPL’s mission trailer for Juno’s dramatic JOI (Jupiter Orbital Insertion)

NASA’s spacecraft Juno (named after the Roman goddess who was Jupiter’s wife and the first to see his true nature) will insert into Jupiter’s orbit two weeks from today.

Juno is particularly aptly named, as it’s rather surprising how little we actually know about Jupiter. At present our knowledge of its further neighbour Saturn is much more complete. So why is that?

Only a handful of spacecraft have visited Jupiter before, mainly fly-by missions – two Pioneers, two Voyagers, Cassini and most recently New Horizon’s on its way to Pluto.

Only one mission, Galileo, has stopped for a tour. Although Galileo was a great success and has told us most of what we know about Jupiter’s large moons, it didn’t manage to answer as many questions as had been hoped on Jupiter itself.

Much of this was down to the extremity of the environment that Galileo encountered every time it got close to Jupiter. The radiation field there is awesomely powerful, sustained by the gas giant’s magnetic field.

Galileo discovered just how big this was - if you could see the magnetic field of Jupiter, it would be bigger than our sun in the sky. This radiation caused severe damage to many of Galileo’s instruments, sending engineers back to the drawing board after every close approach.

Now, 13 years after Galileo ended its mission by plunging into Jupiter, we’re nearly back. This time, the Juno spacecraft has been designed to withstand the expected radiation field with its electronics vault held within strong radiation shielding.

It is hoped that this, along with the specially designed trajectory that will only pass briefly each time through the ‘danger areas’, will allow the spacecraft to survive through the 37 orbits planned.

Jupiter’s ever shifting radiation belts, as imaged by the Cassini spacecraft as it passed on its way to Jupiter. NASA-JPL

Why is it so important to know more about Jupiter? Well, it really does hold most of the ‘stuff’ in the solar system, the very material that we all evolved from. Jupiter is thought to be mainly a ball of hydrogen and helium, and studying how the composition varies as you delve deeper into its clouds will give us a picture of how the planet and the rest of us have evolved.

A detailed weather report from Juno, like seeing how the giant red spot is dissipating, will help us understand some of the interior dynamics of Jupiter. Weather or not this are related to deeper process that drive the awesome magnetic field, is yet to be seen.

Jupiter’s shrinking red spot, as imaged by the Hubble Space Telescope over a number of years. NASA-HST

Juno will also investigate how mass is distributed through the planet. The hope is that, through measuring the gravity field of Jupiter to unprecedented precision, that we can work out weather or not Jupiter has a solid core.

The next challenge from this would be to work out what material would resist the incredible temperatures and pressure expected at this point. One hypothesis is that this is metallic hydrogen, but this is a substance we’re yet to see in the laboratories here on Earth.

All being well, Juno will see no fireworks on July 4th, only the stately clouds of the giant planet below.

Compared to many other current NASA missions, its time-line is short. This solar-powered spacecraft will plummet into Jupiter in 2018. But the hope is that its findings could be on the grandest scale indeed.

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